One of the most promising predictors of the development of human anxiety disorders and depression is extreme behavioral and social inhibition (BI) which is evident prior to adulthood. Studies in human and nonhuman primates demonstrate that individuals with extreme BI commonly have increased reactivity of stress-related systems such as the hypothalamic-pituitary-adrenal axis and the amygdala. While significant advances have been made in understanding BI, its specific pathophysiological mechanisms remain unknown. Studies using non-human primate models of BI are valuable because monkeys display a temperamental disposition that closely maps onto human behavior. However, for various reasons, primate models are not ideal for performing in-depth mechanistic studies. In this regard, rodent models are advantageous as molecular and genetic approaches can be used to establish putative novel mechanisms which can be tested by manipulating specific brain regions with the administration of selective pharmacological agents. It is our contention that further progress in understanding the molecular basis of extreme BI can only be achieved by using an integrative, cross species approach that combines the advantages of both the rodent and non-human primate models to identify brain systems and molecular mechanisms involved in mediating this early risk factor for the development of anxiety and depression. Our laboratory has extensive experience with both non-human primate and rodent models of BI. In our rhesus monkey model there is a physiological correlate of BI as evidenced by a trait-like elevated pattern of brain circuit activity that includes the amygdala that is predictive of a highly anxious temperament. Our rodent studies selecting rats and mice that display a trait-like disposition to engage in extreme BI in response to predator exposure, provide evidence for a phenotype that is analogous to that associated with the human risk to develop anxiety and depression. In this proposal, we will bring together results from both model species using microarray technology to identify genes that are associated with the extreme BI temperament that are shared between rhesus monkeys and mice. The power of this approach is that it will allow us to exploit the relative ease of using mice to identify genes of interest and to perform mechanistic studies while at the same time using data from primates to verify that the genes identified in mice are relevant to primate and human BI. It is important to underscore that while extreme BI is a risk factor for the development of stress-associated psychopathology, only a subset of individuals with this temperament will develop psychiatric illnesses. Therefore, we will also use mice to begin to understand how the genes identified as being associated with extreme BI are related to the vulnerability of extreme BI individuals to develop psychopathology when exposed to chronic social stress. Ultimately the proposed studies will provide insight into the mechanisms that confer susceptibility to psychopathology in at-risk individuals. PUBLIC HEALTH RELEVANCE: Human studies have demonstrated the importance of extreme behavioral inhibition as a temperamental disposition that serves as an early vulnerability marker for the development of anxiety disorders and depression. The proposed experiments will identify novel genes systems that mediate this extreme temperament by combining molecular studies on our adolescent mouse and monkey models of behavioral inhibition. Ultimately, these studies will provide new insights into brain mechanisms mediating the risk to develop anxiety and depressive disorders.